Russian President Vladimir Putin’s underground rival, Alexei Navalny, has led an online crusade aimed at exposing the secret, illicit wealth of Russian officials and oligarchs in slick, snarky, investigative videos.

Turns out his YouTube channel has some powerful viewers in Washington, D.C.: Republican senators.

A group of four senators, including Marco Rubio of Florida, released a little-noticed letter last week encouraging the Treasury Department to target two of Putin’s top cronies who’ve been targeted by Navalny’s infamous videos. The senators even cited some of the investigations.

“We would like to draw your attention to individuals from President Vladimir Putin’s inner circle who have been linked by Russian and international press reports and anticorruption investigators to significant acts of corruption,” the senators wrote. “Some of their dealings have involved U.S. persons and shares of U.S. companies raising the possibility of violations of the Foreign Corrupt Practices Act.”

The first is Putin’s top cop, General Prosecutor Yuri Chaika, who's reputed to have played a role in setting up the infamous June 2016 meeting between Donald Trump Jr. and a Russian lawyer at Trump Tower during the U.S. presidential campaign.

Russian President Vladimir Putin’s underground rival, Alexei Navalny, has led an online crusade aimed at exposing the secret, illicit wealth of Russian officials and oligarchs in slick, snarky, investigative videos.

Turns out his YouTube channel has some powerful viewers in Washington, D.C.: Republican senators.

A group of four senators, including Marco Rubio of Florida, released a little-noticed letter last week encouraging the Treasury Department to target two of Putin’s top cronies who’ve been targeted by Navalny’s infamous videos. The senators even cited some of the investigations.

“We would like to draw your attention to individuals from President Vladimir Putin’s inner circle who have been linked by Russian and international press reports and anticorruption investigators to significant acts of corruption,” the senators wrote. “Some of their dealings have involved U.S. persons and shares of U.S. companies raising the possibility of violations of the Foreign Corrupt Practices Act.”

The first is Putin’s top cop, General Prosecutor Yuri Chaika, who's reputed to have played a role in setting up the infamous June 2016 meeting between Donald Trump Jr. and a Russian lawyer at Trump Tower during the U.S. presidential campaign.

The second is mega-rich oligarch Alisher Usmanov, who once owned a large stake in Facebook and now co-owns the UK soccer team Arsenal.

The letter, in fact, urges Treasury officials to consider allegations made by Navalny’s Anticorruption Foundation and other third-party investigations as they prepare a sanctions-related document set to be released next week, dubbed The Kremlin Report. That report — which has prompted a general freakout and lobbying campaign from the oligarch set — promises to paint a potentially unflattering portrait of rich Russians’ business empires, family wealth, relationship with the Kremlin, and “indices of corruption.”

While The Kremlin Report won’t trigger automatic penalties, those unlucky enough to find themselves in its pages could be shunned by large Western financial institutions, experts told VICE News.

It remains to be seen, however, what the real impact of the report will be — and how much will be released to the public. But one thing is clear: the shout-out to Navalny from Capitol Hill won’t sit well with Putin, who’s dismissed Navalny as a destabilizing rabble-rouser and pointedly refuses to mention his name in public.

Forbidden to run for president and exiled from Kremlin-dominated national television, Navalny has made YouTube videos a key weapon in his fight to undermine Putin.

In late 2015, Navalny’s Anticorruption Foundation released a video called Chaika purporting to document links between the Russian Prosecutor General, his sons, their business empire, a luxury spa hotel in Greece and a murderous Russian criminal gang. Chaika has dismissed the film as “baseless” and “mendacious.”

The Senators’ letter also cited claims made about Usmanov in Navalny’s most-watched video, which took aim at Russian Prime Minister Dmitry Medvedev.

That video purports to document a network of secret luxurious assets, including a fabulous Italian villa, linked to Medvedev through a murky network of foundations and intermediaries — with the participation, allegedly, of Usmanov.

Read: Putin’s archrival has weaponized YouTube and turned it against the Kremlin

“As detailed in an investigation by the Anticorruption Foundation, Mr. Usmanov recently donated an estimated $85 million mansion in Moscow to a foundation with direct links to Russian Prime Minister Dmitri Medvedev,” the letter said. “This has been widely viewed as a form of bribery.”

Usmanov filed a suit against Navalny in Russian court, which ruled in his favor and forced Navalny to remove the video.

Navalny, meanwhile, once again found himself on the wrong end of Russian law. On Monday, Russian courts ordered the closure of a foundation the Putin agitator has used to raise funds for the offices he’s opened in 84 regions across the country.

The ruling, which threatens Navalny’s ability to promote his platform, comes a week before his planned nationwide rally on Sunday, January 28, in support of his election boycott.